Apparatus and methods for runout compensation

ABSTRACT

A runout compensator is provided that angulates a face surface by adjusting two members whose mating surfaces have been machined to slant relative to the central axis of each member. A first member has a shaft over which slides the second member so that the mating surfaces of each member come into and are maintained in contact. Rotating the second member about the shaft of the first member varies the angulation of a face surface. Correctly adjusting the runout compensator, which is attached to a lathe, and a load plate assembly providing biasing to hold the workpiece between itself and the runout compensator, allows the workpiece to be firmly held in the angled position needed to compensate for the runout in the workpiece as the workpiece is turned upon a lathe.

This application is a continuation of U.S. Ser. No. 08/283,775, filedAug. 1, 1994, by James A. Road, entitled "Apparatus and Methods forRunout Compensation " now U.S. Pat. No. 5,615,589.

This invention relates to a method and apparatus for compensating forthe uneven surface of a workpiece, and more particularly for using arunout compensator to hold workpieces upon a lathe to thereby compensatefor runout in the workpiece.

BACKGROUND OF THE INVENTION

Disc brake systems are used on many vehicles and usually employ a rotorand a hydraulic caliper system that force brake pads against the rotorto slow the velocity of the vehicle. Often the axis of the rotor is notperfectly aligned (e.g., perpendicular) with the brake caliper. Unevenwear is thus caused on the surfaces of the rotor as the pads of thebrake caliper are applied to the misaligned rotor. Similarly, improperuse of brakes may cause overheating of the rotor, increasing thelikelihood that the rotor's surfaces may become warped or develop highand low spots. Uneven wear, or runout as seen by the brake caliper, onthe rotor's surfaces is undesirable as it causes squealing, pedalpulsation, vibration and otherwise decreases the efficiency and life ofa disc brake system.

Conventionally, unevenly worn rotors are removed and turned or machinedon a lathe, such as the precision bench lathes provided by AccuIndustries, Inc. of Richmond, Va. Before machining, the rotor isconstrained so that the axis (center line) of the rotor is parallel tothe arbor (axis) of the lathe, a process known as "truing." A machiningtool is located perpendicular to the spindle of the lathe. Upon securingthe rotor with a centering cone and bell clamps, the machining tool isbrought into contact with the surface of the rotor. Machining the rotorin this way results in a rotor whose surfaces are perpendicular, ortrue, to the axis of the rotor.

However, when the machined rotor is replaced on a vehicle whose axle isnot perfectly perpendicular to the brake caliper, the brake caliper willbe misaligned with the surface of the rotor rather than in the desiredparallel relation. The surfaces of the rotor will be skewed with respectto the brake pads of the caliper, which will therefore bear harder orsofter on particular portions of the rotor as the brakes are operated.As a result, the brake caliper pads will simply reintroduce into thebrake rotor the same undesirable unevenness that was removed bymachining, or turning, the rotors. This results in a decreased life ofthe rotor, decreased brake system efficiency and concomitant increasedcosts in maintaining the vehicle's brake system. Potentially, thisproblem could be solved by simply assuring that the calipers areproperly aligned with the vehicle's axis. Such precision is, however,difficult to achieve and costly to implement.

For brake rotors with uneven surfaces, the typical solution to theseproblems was to tilt the rotor about its axis so that its surfaces wereparallel with the machining tool by providing shims between the holdingclamps and the rotor. Essentially, the rotor is shimmed out so that itsposition on the lathe in relation to the machining tool is exactly thesame as the rotor's position on the vehicle's axis in relation to thebrake calipers. Numerous deficiencies are inherent in this approach,including the potential for misjudging the size of shim needed, with theresult that it may cause greater or lesser skew in the rotor than isrequired to compensate for the runout, or the shim may loosen and becomea dangerous flying object should the turning lathe cast it off.Similarly, the shim could be overly large and overlap into the areabeing resurfaced. Moreover, shims decrease the efficiency of the clamps,and as the lathe turns the unsatisfactorily constrained workpiece and acutting or machining tool is applied, the workpiece likely will move outof its skewed position in which runout can be compensated. Consequently,if the workpiece shifts during machining runout is not compensated or,if the shift is sufficiently great, the workpiece could be dangerouslyejected from the lathe.

In any event, shims, being merely an imprecise stop-gap for compensatingfor uneven surfaces, require expenditure of significant trial and errortime and labor in selecting for each brake rotor the correctly sizedshim. Moreover, because shims do not provide any way continuously tovary the amount of unevenness or runout that is being compensated, theuser may have to try various shim sizes before the uneven surface of abrake rotor is fully compensated. In short, placing shims correctly intothe clamp holding the brake rotors is an awkward, time consuming andunsafe procedure.

SUMMARY OF THE INVENTION

The present invention offers a method of operating a runout compensatorapparatus so that objects with uneven surfaces may be firmly held andmachined within a lathe. The runout compensator also compensates forrotor runout or unevenness caused by the misalignment (i.e., skewrelation) between the rotor's surfaces and the brake caliper.

The runout compensator has a first member, such as an inner ring, thatmates with a second member, such as an outer ring. The mating surfacesof the inner and outer rings are machined so that they are notperpendicular to the axis of the rings (i.e., the mating surfaces slantor tilt relative to the rings' axes). One of the rings has a shaft ontowhich the second ring fits and about which the second ring may twistrelative to the first ring. When the two rings are joined with theirmating surfaces in contact, two face surfaces are available. One of theface surfaces is a reference surface; the other of the face surfaceswill angulate as the rings are twisted. Thus, in a starting, trueposition, the machined mating surfaces match so that the angulatingsurface of the entire compensator is perpendicular to the arbor. As therings are twisted out of the true position, the angulating surface ofthe runout compensator "angulates" (moves out of perpendicular relationwith the axis of the arbor) since the machined mating surfaces combineto cause angulation (a change in the angular relation of the facesurface to the arbor's axis) of the angulating surface.

Controlling the angulation of the angulating surface by twisting therings relative to one another allows the clamps to hold the brake rotorin the position needed in order to emulate the runout seen by the brakecaliper without the necessity of impractical, inefficient andpotentially dangerous shims. Reading match marks on the face of thecompensator allows the user to determine the setting needed to providethe desired amount of runout. A chart translating the setting of thematch marks into the amount of runout compensation provided for eachparticular brake rotor size may further simplify the adjustment forrunout.

However, before using the runout compensator, the user first determinesthe amount of runout in the rotor needed to be compensated. This isaccomplished by, among other methods, placing the rotor on the lathe andmachining approximately a one inch (1") swath near the edge of the rotorwithout the compensator, thereby "truing" that swath of the rotorsurface (i.e., making the machined area perpendicular to the axis of therotor). Then the rotor is reattached to the vehicle and the usermeasures the highest and lowest portions of the rotor relative to themachined area.

After marking the high spot of the rotor, it is removed and mounted on alathe with the runout compensator, clamps and a load plate assembly,which applies bias to maintain the rotor firmly between the clamps.Although a conventional centering cone with a spring of higher tensioncould be used to compress the rotor, bell clamps and runout compensatortogether, potentially the rotor could wobble if the tension isinsufficient. The load plate assembly prevents such wobbling, thusmaintaining the rotor in the correct reference position necessary toinduce the proper degree of runout.

The runout compensator is then adjusted, making sure that its matchmarks are aligned with the high spot marked on the rotor, which assuresthat the angulation created by the runout compensator will correctlyinterface with the uneven surfaces of the rotor so that those surfacesare tilted to be parallel with the machining tool. After adjustment ofthe runout compensator, the load plate assembly's set screw (whichprevents the load plate assembly from rotating about the arbor as therunout compensator is adjusted) is loosened, the arbor nut is tightenedand the rotor is ready for machining. Greater efficiency, simplicity andsafety is accordingly offered by the present invention since, amongother improvements, clamps need no longer be shimmed to create runoutand thus can better interface with the rotor or other workpiece.

It is therefore an object of this invention to provide a method forcompensating for the uneven surface of a workpiece.

It is accordingly another object of the present invention to provide arunout compensator that can adjustably angulate a face surface.

It is an additional object of the present invention to provide a runoutcompensator for interfacing a workpiece and a lathe and compensating forrunout in a workpiece, such as a disc brake rotor.

It is another object of the present invention to offer a method ofquickly and efficiently operating the runout compensator with a lathe.

It is yet another object of the present invention to more firmly, andthus with increased safety, hold a workpiece to be machined upon alathe.

It is a further object of this invention to provide for a lathe, arunout compensator and load plate assembly, which together interfacewith and hold firmly for machining various workpieces in which it isnecessary to compensate for runout by tilting the workpiece anappropriate amount.

Other objects, features and advantages of this invention will becomeapparent with reference to the remainder of this document.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a lathe equipped with a runout compensator anda load plate assembly of the present invention.

FIG. 2 is a perspective view of the invention shown in FIG. 1.

FIG. 3 is an exploded perspective view of one embodiment of a runoutcompensator.

FIG. 4 is a diametrical cross sectional view of the runout compensatorshown in FIG. 3 whose rings are set in a true position.

FIG. 5 is a diametrical cross sectional view of the runout compensatorshown in FIG. 3 whose rings are angulated to compensate runout.

FIGS. 6 and 7 are top views of the rings of the runout compensator shownin FIGS. 3-5.

FIG. 8 is an exploded perspective view of a load plate assembly usedwith the runout compensator of the present invention.

FIG. 9 is a side view of an assembled load plate assembly shown in FIG.8.

DETAILED DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 illustrate a lathe 10 having a headstock through which aspindle 12 passes and against which an arbor 19 is secured. Suspendedfrom the arbor 19 is a brake rotor 20 defining a first side 22 and asecond side 24. Brake rotor 20 is held firmly fixed by a first bellclamp 14, extending through an aperture in the first side 22, and asecond bell clamp 16, each bearing against a circular skirt 26 attachedto the second side 24. Within the first bell clamp 14 may be located acentering cone (not shown) that is biased away from the first bell clamp14 to center the rotor in a true (perpendicular) relation to the arbor19. Pressure is applied to clamp firmly the rotor 20 between the firstand second bell clamps 14, 16 by adjusting load plate assembly 30 toapply pressure to first bell clamp 14, which thereby pushes rotor 20 andsecond bell clamp 16 against the runout compensator 50 that is locatedadjacent the headstock of the lathe 10.

Components of the runout compensator 50 are shown perhaps best in FIG.3, illustrating an exploded perspective view of a first ring 52, asecond ring 54 and a clip 60. First ring 52 defines a first matingsurface 66 and a bore 62 through which will pass the arbor 19 and ashaft 56, which supports the second ring 54. Second ring 54 defines asecond mating surface 68 and, directly opposite, a recessed shelf 55.Each of the first and second mating surfaces 66, 68 is machined, groundor otherwise manipulated to tilt or slant so that they are notperpendicular to the axis of their respective first and second rings 52,54.

One embodiment of runout compensator 50 is produced by sliding thesecond ring 54 over the shaft 56, then placing the clip 60 into acircular channel 58 that surrounds the shaft 56. The runout compensator50 defines a front face 74 and a rear face 72, each of which areperpendicular to the central axis of their respective rings. Wave washer61 may be located between the clip 60 and the recessed shelf 55 to actas a spring to maintain contact between the first and second rings 52,54, as shown in FIGS. 4 and 5. Clip 60, with wave washer 61, maintainssufficient pressure against the recessed shelf 55 to cause the firstmating surface 66 to maintain contact with the second mating surface 68.Although the first and second rings 52, 54 should be manufactured to fitclosely with one another, use of the wave washer 61 allows some variancein manufacturing tolerances since the bias of the wave washer 61 willforce the first and second rings 52, 54 together. Such contact ismaintained even when the first ring 52 and the second ring 54 aretwisted or rotated with respect to one another by hand or, when moremechanical advantage is required, by using spanner wrenches to applytorque to the first and second rings 52, 54 through several cavities 64located on their perimeters.

FIG. 4 illustrates the runout compensator 50 set in a first, trueposition so that a front face 74 is perfectly perpendicular with thecentral axis of the bore 62. In contrast, FIG. 5 illustrates the runoutcompensator 50 set to compensate runout, which is indicated by an area51. (The dimensions provided are for illustrative purposes only). Bytwisting the first ring 52 relative to the second ring 54, the frontface 74 is moved between a true position (zero slant) and a maximumrunout position (maximum slant) because the slant machined into thefirst and second mating surfaces 66, 68 adds together and is translatedto the front face 74 as the first and second rings 52, 54 are twisted.

In the maximum runout position shown in FIG. 5, the front face 74defines a plane surface that crosses skew to the central axis of thebore 62. Because the bore 62 will rest upon the arbor 19 of the lathe10, the slanted plane surface defined by the front face 74 also willcross skew to the arbor 19. However, a rear face 72 of the runoutcompensator 50 may define a plane directly perpendicular to the axis ofthe bore 62 (and thus the arbor 19) which allows the runout compensator50 to interface with the shoulder of the arbor 19. Angulation attainedby adjusting the second ring 54 with respect to the first ring 52 isthus translated to only the front face 74.

Attaching a bell or other type clamp to the front face 74 after correctangulation is achieved provides excellent surface contact (uninterruptedby shims) with the rotor 20 and tilts the rotor 20 to the positionneeded to compensate for the runout in the rotor 20 as it is machined.(Because there is space, or play, between the arbor 19 and the rotor 20,it can be tilted with respect to the arbor 19). Instead of butting thebell clamp 14 against the face surface of the runout compensator 50, thebell clamp 14 or another clamp can be directly attached to theappropriate face surface so that adjusting the runout compensatorangulates the attached clamp.

Rear face 72 is held against the shoulder of the arbor 19 by the forceproduced by the load plate assembly 30, which has an outer plate 34, aninner plate 36 and a spring 38. Each of the outer and inner plates 34and 36 respectively define an outer shoulder 35 and an inner shoulder37, and together define a central bore 40 through which will pass thearbor 19. A threaded hole 31 holds a set screw 32 that may be tightenedto bear against the arbor 19 and thereby prevent the rotation of theload plate assembly 30 about the arbor 19. Spring 38 exerts bias againstthe outer plate 34 and the inner plate 36 by exerting force against theouter shoulder 35 and the inner shoulder 37, respectively.

A retaining bolt 42 prevents the spring 38 from separating completelythe outer and inner plates 34, 36. Partially threaded retaining bolt 42slips into a hole 44 in the face of the inner plate 36. Hole 44 definesa shelf against which bears the head of the retaining bolt 42. Thethreaded end of the retaining bolt 42 threads into a threaded depression46 bored in one face of outer plate 34 to prevent the spring 38 fromforcing the inner plate 36 completely away from the outer plate 34.Loosening the retaining bolt 42 allows the inner plate 36 to be biasedfarther away from the outer plate 34 by the spring 38; tightening theretaining bolt 42 limits the amount of separation provided and thecorresponding amount of bias available. The bias adjustably forces thesecond bell clamp 16 against the rotor 20, which in turn pushes againstthe first bell clamp 14 that interfaces with the front face 74 of therunout compensator 50. Because the runout compensator 50 is fixed byvirtue of the rear face 72 bearing against one end of the arbor 19, theforce produced by the load plate assembly 30 acts to compress the rotor20 between the first and second bell clamps 14 and 16.

Other shapes may be used in place of the first and second rings 52, 54for the runout compensator 50 so long as the desired amount of runout isreproduced. The circular shape of rings 52, 54 does, however, offer anadvantage in that the runout produced by twisting or rotating the rings52, 54 can more easily be matched with the runout in the actual rotor 20being machined upon lathe 10. For example, match marks 70 can beprovided on first and second rings 52, 54 in order to indicate to theuser the amount of runout provided upon twisting the rings 52, 54relative to one another.

For instance, as shown in FIG. 4, when the first and second rings 52, 54are positioned so that the match marks 70 read 0-0 (not shown), the userwill be assured that the runout compensator 50 is set in the trueposition (i.e., has face surfaces perpendicular to the arbor 19). Achart can be provided to show the user the degree of angulation oramount of displacement provided when the first and second rings 52, 54are twisted to align the match marks 70 in the 0-0, 1-1, 2-2, 3-3, 4-4,5-5, 6-6 or other position. A set of the match marks 70 is illustratedat FIGS. 6 and 7 with each numeral corresponding to its counterpart onthe first or second ring 52, 54. As the numerals increase, so does thedegree of slant as measured from the reference point (i.e., the pointindicated by numeral 0) and the point indicated by the particularnumeral. Thus, the point indicated by 3 has more slant than the pointindicated by 2, but less slant than the point indicated by 4.

Having already calculated the runout (either the linear differencebetween the surfaces of the rotor 20 and the machined swath or theangulation of the surfaces of rotor 20 in relation to true), the usercan use the known values of slant or tilt created by the runoutcompensator 50 when the match marks 70 are aligned in particularcombinations, thereby allowing runout to be properly matched. Knowingthe angulation or displacement provided by the runout compensator 50when the match marks 70 are aligned in a particular relationship allowsthe user to adjust the runout compensator 50 to compensate properly forthe previously determined runout in the rotor 20.

There are numerous ways to tilt or angulate the runout compensator'sfront face 74 to match the desired runout. First, the front face 74 canbe angulated to slant at an angle matching the angular runout of thesurfaces of the rotor 20. Second, the actual linear displacement of thefront face 74 from a reference point can be calculated (i.e., the "high"and "low" points of the front face 74 relative to true). This lineardisplacement is then matched with the linear displacement determined bymeasuring the high and low spots on the surfaces of the rotor 20.

However, if (as is normally the case) the radius of the front face 74 isdifferent from the radius of the rotor 20, there will not be aone-to-one correspondence between the linear displacement of the frontface 74 and the linear measurement of runout in the rotor 20. Althoughthe linear measurements can be reconciled by application oftrigonometric equations, such calculations are difficult and timeconsuming. Thus, instead of laboriously calculating the runout ordisplacement at which to set the runout compensator 50 for a particularsized rotor 20 having a particular amount of runout, a chart can alsoshow that information for each particular rotor size (i.e., an 8-inch,10-inch or 12-inch diameter rotor). For instance, the chart could showthat 0.003" (three thousandths of an inch) runout at the edge of an 8"(eight inch) diameter rotor corresponds to a 3-3 match mark 70 settingon the runout compensator 50 and the same runout on the edge of a 12"(twelve inch) diameter rotor corresponds to a 2-2 setting. Standardinterpolation calculations allow the user easily to derive any settingsnot shown upon the chart.

Operation of the runout compensator 50 is accomplished by firstmachining a portion of the rotor 20 to establish a "true" referencesurface to measure from and then replacing the rotor 20 onto the vehiclein its original position. The runout of the rotor 20 is measured whileit is on the vehicle and marking both the high spot on the outside faceof the rotor 20 and the original position of the rotor 20 are marked.Rotor 20 is then removed from the vehicle and remounted on the lathe 10.Load plate assembly 30 is adjusted by screwing the retaining bolt 42until only a fraction (e.g., 1/32) of an inch is visible between theouter and inner plates 34, 36. The set screw 32 is locked down toprevent the load plate assembly 30 from rotating as the runoutcompensator 50 is adjusted. The high mark on the rotor 20 is thenaligned with match marks 70 on the runout compensator 50. Generally,alignment is accomplished by holding the rotor 20 and using a spannerwrench on the inside nearest to the second ring 54 of the runoutcompensator 50 and rotating the runout compensator 50 until it isaligned with the high mark.

Using two spanner wrenches, the runout compensator 50 is then adjustedto angulate the front face 74 to compensate the runout. As the runoutcompensator 50 is adjusted, the user may be required to realign thematch marks 70 with the high spot marked on the rotor 20, as describedabove. The amount of angulation can be determined by the methodspreviously described, that is through calculation, comparing themeasured runout to a chart showing corresponding match mark settings orestimation. As the front face 74 is tilted by adjustment of the runoutcompensator 50, the bell clamp 14 attached to that front face 74 alsotilts. By holding the rotor 20 firmly against the tilted,non-perpendicular bell clamp 14, the surfaces of the rotor 20 are heldin a parallel relation with the machining tool, despite the runout inthe surfaces of the rotor 20. Once the runout is compensated, the setscrew 32 is loosened, the arbor nut 18 is tightened and the rotor 20 ismachined.

The rotor 20 is then remounted on the vehicle in its original position(matching the mark indicating the high spot and the mark showing theoriginal position). Because the brake calipers of the runout compensator50 are no longer misaligned with the surfaces of the rotor 20 and willnot wear down the rotor 20 as quickly, the brakes will achieve generallyhigher efficiency.

The foregoing is provided for purposes of illustrating, explaining anddescribing one embodiment of the present invention. Modifications andadaptations to the described embodiment will be apparent to those ofordinary skill in the art and may be made without departing from thescope or spirit of the invention and the following claims.

What is claimed is:
 1. A runout compensator, comprising:(a) a male ringpenetrated by a male ring bore, said male ring including a male rindouter face; a substantially planar male ring mating surface skewedrelative to said longitudinal axis of said male ring bore; and a shaftprojecting from said male ring mating surface, said shaft penetrated bysaid male ring bore; and (b) a female ring received by said male ring,said female ring penetrated by a female ring bore, said female ringincluding a female ring outer face; and a substantially planar femalering mating surface skewed relative to said longitudinal axis of saidfemale ring bore, said female ring adapted to receive said male ringshaft to allow said female ring to rotate relative to said male ring,whereby abutment of said male ring mating surface and said female ringmating surface against each other cause said male ring outer face toangulate relative to said female ring outer face.
 2. The compensator ofclaim 1 in which the female ring further comprises a cavity in saidfemale ring outer face, said cavity adapted to accommodate a retainerfor retaining said female ring on said male ring.
 3. The compensator ofclaim 2 further comprising a retainer.
 4. The compensator of claim 1wherein:(a) said male ring outer face and said substantially planar malering mating surface of said male ring cooperate to cause said male ringthickness to vary about the periphery of said male ring, therebycreating a male ring maximum thickness radius, and a male ring minimumthickness radius located substantially diametrically from said male ringmaximum thickness radius; (b) said female ring outer face and saidsubstantially planar female ring mating surface of said female ringcooperate to cause said female ring thickness to vary about theperiphery of said female ring, thereby creating a female ring maximumthickness radius, and a female ring minimum thickness radius locatedsubstantially diametrically from said female ring maximum thicknessradius; (c) wherein, when said male ring maximum thickness radius issubstantially aligned with said female ring minimum thickness radius,said male ring outer face is substantially parallel with said femalering outer face.
 5. A runout compensator, comprising:(a) a male ringpenetrated by a male ring bore, said male ring including a male ringouter surface; a substantially planar male ring mating surface; one ofsaid surfaces skewed relative to said longitudinal axis of said malering bore; and a male ring shaft projecting from said male ring matingsurface, said shaft penetrated by said male ring bore; (b) a female ringreceived by said male ring, said female ring penetrated by a female ringbore, said female ring including a female ring outer face and asubstantially planar female ring mating surface, one of said surfacesskewed relative to said longitudinal axis of said female ring bore, saidfemale ring adapted to receive said male ring shaft; (c) said male ringouter surface and said male ring mating surface cooperate to cause saidmale ring thickness to vary about the periphery of said male ring,thereby creating a male ring maximum thickness radius, and a male ringminimum thickness radius; (d) said female ring outer surface and saidfemale ring mating surface cooperate to cause said female ring thicknessto vary about the periphery of said female ring, thereby creating afemale ring maximum thickness radius, and a female ring minimumthickness radius; (e) wherein, when said male ring maximum thicknessradius is substantially aligned with said female ring minimum thicknessradius, said male ring outer surface is substantially parallel with saidfemale ring outer surface and wherein abutment of said male ring matingsurface and said female ring mating surface against each other causesaid male ring outer surface to angulate relative to said female ringouter surface as the rings are rotated relative to each other.
 6. Acompensator according to claim 5 further including markings on aperiphery of at least one of said male ring or said female ring, saidmarkings adapted to indicate relative skew between said outer surfacesof said male ring and said female ring.
 7. A compensator according toclaim 5 further comprising a cavity in at least one of said rings, saidcavity adapted to accommodate a retainer for retaining said male ringand said female ring substantially together.
 8. A compensator accordingto claim 5 further comprising a biasing structure for applying relativebias between said male ring and said female ring, in order at least tocreate friction between said male ring and said female ring.
 9. Acompensator according to claim 5 further comprising a retainer forretaining said male and female ring substantially together and forapplying relative bias between said male ring and said female ring inorder to create friction between said male ring and said female ring.10. A compensator according to claim 5 in which the maximum thicknessradius of at least one of said rings is located substantiallydiametrically from said minimum thickness radius.